Fuel supply control system for an internal combustion engine

Abstract

An internal combustion engine has a combustion chamber and an air passage leading to the combustion chamber for conducting air to the combustion chamber. A throttle valve is disposed in the air passage for adjusting the rate of air flow into the combustion chamber. A compressor is disposed in the air passage at a point upstream of the throttle valve for compressing the air. A flow meter is disposed in the air passage at a point upstream of the compressor for sensing the rate of air flow through the air passage. Fuel is injected into the air passage at a point downstream of the throttle valve. The rate of fuel injection normally has a preset relationship with the sensed air flow rate. When the throttle valve is closed, the fuel injection rate is limited to no more than a predetermined level regardless of the preset relationship between the fuel injection rate and the sensed air flow rate. In the case of periodic fuel injection at a frequency proportional to engine speed, the amount of fuel injected during each fuel injection stroke may be limited to a predetermined level when the throttle valve is closed.

What is claimed is: 
     
       1. A fuel supply control system for an internal combustion engine having a combustion chamber, an air passage leading to the combustion chamber for conducting air to the combustion chamber, a throttle valve disposed in the air passage for adjusting the rate of air flow into the combustion chamber, and a compressor disposed in the air passage at a point upstream of the throttle valve for compressing the air, the system comprising: (a) a flow meter disposed in the air passage at a point upstream of the compressor for sensing the rate of air flow through the air passage;   (b) first means, responsive to the flow meter, for injecting fuel into the air passage at a point downstream of the throttle valve at a rate having a preset relationship with the sensed air flow rate;   (c) second means for sensing whether or not the throttle valve is closed; and   (d) third means, responsive to the second means, for limiting the fuel injection rate to no more than a predetermined level regardless of the preset relationship between the fuel injection rate and the sensed air flow rate when the throttle valve is closed.   
     
     
       2. The system of claim 1, further comprising fourth means responsive to the second means for measuring elapsed time since the moment of closing of the throttle valve, and fifth means responsive to the fourth means for determining whether or not the elapsed time exceeds a preset time value, the third means responsive to the fifth means and operable to maintain the limitation on the fuel injection rate as long as the elapsed time does not exceed the preset time value and the throttle valve remains closed. 
     
     
       3. A fuel supply control system for an internal combustion engine having a combustion chamber, an air passage leading to the combustion chamber for conducting air to the combustion chamber, a throttle valve disposed in the air passage for adjusting the rate of air flow into the combustion chamber, and a compressor disposed in the air passage at a point upstream of the throttle valve for compressing the air, the system comprising: (a) a flow meter disposed in the air passage at a point upstream of the compressor for sensing the rate of air flow through the air passage and generating a signal indicative thereof;   (b) first means for sensing the rotational speed of the engine and generating a signal indicative thereof;   (c) second means, responsive to the air flow rate signal and the engine speed signal, for periodically injecting fuel into the air passage at a point downstream of the throttle valve at a frequency proportional to the engine speed, the amount of fuel injected during each fuel injection stroke having a preset relationship with the air flow rate and the engine speed;   (d) third means for sensing whether or not the throttle valve is closed and generating a signal indicative thereof; and   (e) fourth means, responsive to the throttle valve signal, for limiting the amount of fuel injected during each fuel injection stroke to no more than a predetermined level regardless of the preset relationship of the fuel injection amount with the air flow rate and the engine speed when the throttle valve is closed.   
     
     
       4. The system of claim 3, further comprising fifth means responsive to the throttle valve signal for measuring elapsed time since the moment of closing of the throttle valve, and sixth means responsive to the fifth means for determining whether or not the elapsed time exceeds a preset time value, the fourth means responsive to the sixth means and operable to maintain the limitation on the fuel injection amount as long as the elapsed time does not exceed the preset time value and the throttle valve remains closed. 
     
     
       5. The system of claim 3, further comprising: (a) a temperature sensor for sensing the temperature of coolant of the engine and generating a signal indicative thereof;   (b) an auxiliary passage connected to the air passage and bypassing the throttle valve;   (c) fifth means, responsive to the coolant temperature signal, for adjusting the rate of air flow through the auxiliary passage in accordance with the coolant temperature; and   (d) sixth means, responsive to the coolant temperature signal, for adjusting the predetermined fuel injection level in accordance with the coolant temperature.   
     
     
       6. A method of controlling fuel supply to an internal combustion engine of the type having a supercharging compressor driving air down an intake duct to the engine, and a throttle valve downstream of the compressor, comprising the steps of: (a) monitoring the position of the throttle valve;   (b) monitoring the rate of air flow through the intake duct at a point upstream of the compressor;   (c) deriving a desired fuel injection rate from the monitored air flow rate on the basis of a known relationship between the monitored air flow rate and the desired fuel injection rate;   (d) if the throttle valve is in a position blocking the intake duct to the greatest possible extent and the desired fuel injection rate exceeds a threshold value, replacing the derived desired fuel injection rate with the threshold value; and   (e) injecting fuel into the intake duct downstream of the throttle valve at a rate corresponding to the desired fuel injection rate.